The present invention relates to a laminar flow injection molding apparatus and a laminar flow injection molding method. More particularly, the invention relates to such apparatus and method in which casting operation continues as long as molten metal flows in a laminar flow, and turbulent flow can be promptly converted into a laminar flow.
Quality of a casted product produced by an injection molding apparatus, particularly a die-casting machine, is largely dependent on fluidity of the molten metal which is an injected material. For example, if molten metal is turbulently introduced into the cavity, the molten metal flows discontinuously, i.e. , does not fill the cavity at a steady rate. As a result, the molten metal cannot be sufficiently distributed throughout the cavity, since air may be trapped or involved into the molten metal . Consequently, the casted product may not have a uniform mechanical strength over its mass, and may not have sufficient pressure resistance,
Introducing molten metal into the cavity at a continuous laminar flow is therefore necessary. Such factors as injection speed, injection pressure, and variation in injection speed requires careful consideration to obtain the laminar flow. However, determining the fluidity of the molten metal flowing into the cavity is generally difficult.
In order to determine casting conditions required for improving fluidity, Japanese Patent Application Kokai No. sho-56-109154 discloses a die-casting machine. According to the invention, several injection operations are carried out in which the injection plunger is stopped at a different position during each injection operation- The metal mold is opened after the injected molten metal cools and solidifies, and quality in the casted products derived from each stop position is checked to determine fluidity of the molten metal and thus optimum injecting condition.
However, with the invention described in the Japanese Patent Application Kokai No. sho-56-109154, inertial force is imparted on the molten metal depending on the injection speed. Therefore, even if the injection plunger is temporarily stopped during the injection, it is almost difficult to conclude that the molten metal is also stopped at that position. Thus, accurate judgment cannot be made. Further, the molten metal flow can only be indirectly inspected by examining resultant products after casting. Directly observing actual flow to judge whether laminar flow or turbulent flow would be impossible.
Japanese Patent Application Kokai No. sho-59-215259 discloses necessity of high speed injection so as to avoid reduction in temperature of the molten metal, and discloses shifting the injection speed from high speed to low speed immediately before the molten metal enters the cavity to avoid scattering and turbulence of the molten metal, and consequent air involvement, that accompanies high speed injection.
In the invention disclosed in the Japanese Patent Application Kokai No. sho 59-215259, primary attention is directed to the prevention of the molten metal from its turbulent flowing during low speed injection. The disclosed invention does not provide a method for directly determining whether the molten metal has laminar flow or turbulent flow at the time of low speed injection.